Denning ecology of two populations of Asiatic black bears in Nagano prefecture, Japan

We investigated dens, denning chronology, and behavior in dens of Asiatic black bears (Ursus thibetanus) in 2 neighboring study areas in central Nagano prefecture, central Japan. In the first area, which had been only partially affected by logging, 3 out of 4 dens were in hollow trees with elevated entrances. In the second area, which had been 100% affected by logging and where virtually all hollow trees had been removed, 6 out of 6 dens were ground dens. An additional 72 dens of radiocollared bears were in areas we were unable to access due to a combination of steep terrain, deep snow, and distance from roads. The denning period was approximately 5 months, from late November-early December till late April-early May. No bear in a tree den with an elevated entrance left its den during our visits. Females without cubs left their ground dens when visited in December and in April. Females with or without cubs stayed in their ground dens when visited in mid-winter. Females with cubs stayed in their dens when visited in April. Our findings suggest Asiatic black bears in central Nagano prefecture prefer to den in hollow trees with elevated entrances. Forest managers should protect and allow for the recruitment of den trees, as well as assure the seclusion of hibernating bears by limiting access roads in denning areas.